1. Field of the Invention
The present invention pertains to cellular telecommunications, and particularly to determining the radio access technology types available in a cell of a telecommunications network.
2. Related Art and Other Considerations
Cellular telecommunications systems employ a wireless link (e.g., air interface) between the (mobile) user equipment and a base station (BS). The base station has transmitters and receivers for radio connections with numerous user equipment units. One or more base stations are connected (e.g., by landlines or microwave) and managed by a radio network controller (also known in some networks as a base station controller [BSC]). The radio network controller is, in turn, connected through control nodes to a core communications network. Control nodes can take various forms, depending on the types of services or networks to which the control nodes are connected. For connection to connection-oriented, switched circuit networks such as PSTN and/or ISDN, the control node can be a mobile switching center (MSC). For connecting to packet switching data services such as the Internet (for example), the control node can be a gateway data support node through which connection is made to the wired data networks, and perhaps one or more serving nodes.
Today for mobile radio user equipment units there are multiple radio access technology types. Current second generation radio access technology types include the Global System for Mobile communications (GSM), IS-136, IS-95, PDC, and AMPS. Each of these radio access technology types has distinguishing characteristics, such as (for example) differing protocols and differing frequency bands of operation. Moreover, some radio access technology types such as GSM service user equipment units operating in differing frequency bands (1450 MHz, 900 MHz, 1800 MHz, and 1900 MHz for GSM). The differing radio frequency bands may be assigned to different service providers or operators, for example.
A mobile user equipment unit operates in accordance with the particular radio access technology type(s) which it functionally supports. In other words, the radio access technology type(s) in accordance with which a user mobile equipment unit operates is dependent upon capabilities of that particular user equipment unit. Such capabilities concern, in addition to frequency band of operation, factors such as radio frequency power, encryption capability, and (if TDMA) time slot availabilty.
Typically, when a mobile user equipment unit is activated, the user equipment unit attempts to decode a common channel network message (BCCH) transmitted on a frequency band(s) supported by the user equipment unit. The mobile user equipment unit then attemps to use its home system information (such as mobile country code [MCC] and the mobile network code [MNC]) in order to register its location with its home location register (HLR).
The provision of additional services over wireless networks (such multimedia, for example) beckons a third generation of mobile telecommunication technology. With the advent of such services as mobile multimedia, a third generation counterpart will likely be developed for each radio access technology type. For example, a third generation for GSM will be known as UMTS; a third generation for IS-136 is expected to be labeled as xe2x80x9cUWC-136xe2x80x9d; a third generation for IS-95 may carry the designation xe2x80x9cCDMA 2000xe2x80x9d. Such being the case, user equipment units of an entire matrix of user equipment radio access technology types and generations will emerge and be capable of roaming across telecommunications networks. The telecommunications networks themselves will be of diverse radio access technology types and generations.
Thus, there is the prospect of numerous mobile user equipment units (of differing radio access technology types and of differing generations within each type) roaming through telecommunications networks of differing radio access technology types and generations. This will make it complex, time-consuming, and difficult for a user equipment unit to scan all frequency bands, interpret all access technology types, detect and select networks, and finally determine a home network.
The fact of multiple radio access technology type and multiple generations within each type also presents handover problems from one cell to another cell, as not all cells may have the same capabilities (radio access technology types and generations). For example, there may be islands of a third generation UMTS cell in a GSM ocean, in which case a third generation UMTS user equipment may travel from a third generation cell into a second generation cell. Accordingly, in order to make the handover, such situation would have to be anticipated constantly with the third generation UMTS user equipment unit performing handover (e.g., power) measurements relative to frequencies for all generations, and reporting such measurements to a network that may or may not have the capabilities or the commercial rights to handover to these other networks. It would be preferable, if possible, to avoid continually performing handover measurements of an entire matrix of radio access technology types and generations.
Moreover, according to some present techniques, handover measurements are made at a time delay after a slot accorded to a connection. Handover measurements in a large amount of frequency bands would take too long, and could be at potentially conflicting times.
There has been speculation that a beacon frequency, emitted from a base station mutual to plural network operators, could be emitted to apprise all mobile user equipment units of the radio access technology types available in a cell. In accordance with this proposal, upon activation a mobile user equipment unit would first seek the beacon frequency, and from the beacon frequency determine what radio access technology types are available in a cell. However, the beacon frequency proposal requires existence of an independently operated base station, or at least a separate frequency dedicated to providing radio access technology type information.
What is needed, therefore, and an object of the present invention, is provision of a technique whereby a mobile user equipment unit can quickly determine the radio access technology types and generations available in a telecommunications cell.
In accordance with the present invention, a base station broadcasts (e.g., in a BCCH message) a capabilities message which includes a supported service bitmap that is decoded by all user equipment units. For each service (e.g., radio access technology type and generation), the bitmap contains a bit indicating whether that radio access technology type and generation is available from the serving cell (i.e., confirming that coverage exists and selection or handover is possible). In addition, the capabilities message contains one or more preferred network identifiers (PNIs). For example, for GSM the preferred network identifiers can include the mobile country code (MCC) and the mobile network code (MNC) or some form of base station identity code (BSIC). These preferred network identifiers correspond to the preferred network(s) for each available radio access technology type and generation.
Upon receipt of the bitmap, the mobile user equipment unit scans the bitmap to find a radio access technology type and generation which it can utilize, and selects the preferred network, if possible. For the utilizable radio access technology type, the user equipment unit fetches the preferred network identifier from the BCCH broadcast message and uses the preferred network identifier for call set up and registering the location of the user equipment unit.
The present invention also address the handover situation by providing the user equipment unit with information to steer the handover measurements. A handover requirements message broadcast by the network provides the user equipment unit with a bitmap indicating the radio access technology types and generations for which the base station requires the user equipment unit to make handover measurements and reports. The handover requirements message can be on the same or similar channel as the capabilities message, or a specific handover message). Each base station controller or radio network controller knows the capabilities of adjacent base stations in its own network or co-operative networks. For example, for a given third generation base station or cell totally surrounded by third generation base stations, that base station or cell can broadcast (via the handover requirements message) a directive that the user equipments served by that base station or cell make handover measurements only on third generation frequencies. On the other hand, a third generation base station or cell that is at the edge of the third generation network coverage and has adjoining second generation cells, that third generation base station or cell can anticipate that user equipment units may move further toward or into the second generation cells. Therefore, the base station or cell will broadcast (e.g., via its handover requirements message) that user equipment units shall now make also second generation power measurements and reports for potential handover purposes.